Before i played M&M i played a system that has a metric ton of premade adventures by the publisher (300 books. Some of them short adventures, some of them entire campaigns) and alot of fan made adventure books (pdfs to be precise). It's just the normal case to just take one of these and play it. (if you are interrested, it's the german (-> original) version of: http://en.wikipedia.org/wiki/The_Dark_Eye )

Due to that i'm struggeling strongly to write/build/??? adventures for my M&M group. M&M in general and the superhero genre in specific seem only to have 1-2 adventures (incl. the new emerald city), which doesn't seem to be a good fit for my group. I've looked around a bit and found 1-2 adventures back from the 90ties, which are only hardly avaiable. Also drivethrough seems to have a couple of adventures (Time Bomb is really cool as a subplot).

But is that all that is avaiable? Aren't there any fansite communitys of people who wrote superhero themed adventures? Are there no "Write a Superhero themed adventure" contests?

Gimmick's Gadgets has about a dozen free ones for 2E and 3E. As you noted, the RPG sales sites have a few more. Honestly, this is something which comes up periodically on the boards. Adventures are generally a bit of a loss leader in the RPG industry. Companies like TSR used to get them for free from new employees (Tracy Hickman had a good article about how everyone who got hired by TSR was expected to have at least one full adventure module in their portfolio to hand over). Companies like Pathfinder have been able to make their money by adapting the old TSR modules. Outside of that, superhero RPGs have so few limits on the players, so it's hard to address all of the possibilities. And, frankly, digital piracy is enough of an issue that the small margin of profit on adventure modules has shrunk to nothing to negative.

So, long story short, there are adventures out there, but there really is not much of a market, at least not a profitable one, especially for superhero games.

Fuzzyboots is dead on, but if you search these forums, there is no shortage of campaign or story suggestions. Over in roll call are literally hundreds of characters other people have made. Combine those two and that's a wealth of "premade" material at your finger tips